Coherent zirconium silicates



Reissued Oct. 3, 1939 PATENT OFFICE 21,224 COHERENT ZIROONIUM SILICATESCharles J. Kinzie, Niagara Falls, N. Y., assignor to The Titanium AlloyManufacturing Comp ny, New York, N. Y.

, a corporation of Maine No Drawing. Original No. 2,101,947, datedDecember 14, 1937, Serial N0. 682,795, July 29, 1933.

Application for reissue June 2, 1939, Serial No.

11 Claims.

My invention relates generally to the production of coherent zirconiumsilicate masses. Such masses may be employed for filtration purposes,gas dispersions and the like, as well as for abrasive tools andrefractories.

Zirconium silicate, present in nature as the mineral zircon, is amaterial that inherently possesses a high degree of stability andresistance to contact with chemicals, and that also admirably withstandshigh temperatures. When fired at high temperatures, it yields productswhich are highly refractory in nature. In the past, however, certaindifficulties have been experienced in securing proper cohesion of suchmasses. This is particularly true where the masses are porous, that is,Where the particles of zirconium silicate are separated by pores or airspaces.

It is therefore an object of this invention to produce coherent massesof zirconium silicate. Other objects will appear hereinafter.

These objects are accomplished by mixing with zirconium silicate abonding agent comprising a double silicate of zirconium and a metaltaken from the group consisting of alkali metals, alkaline earth metalsand magnesium, or a material which will form such a double silicate atan elevated temperature, and firing said mixture at an elevatedtemperature.

The double silicates of the above class which may be used are sodiumzirconium silicate, potassium zirconium silicate, barium zirconiumsilicate, calcium zirconium silicate and magnesium zirconium silicate. Amaterial which will decompose toform sodium zirconium silicate at anelevated temperature is a solution of sodium zirconium silicon citrate.

The amount of bonding agent used is that necessary to produce therequired eiTect. In the case of sodium zirconium silicon citratesolution it may, for example, vary from 1 to 12 parts by weight of thesolution to 100 parts of granular zirconium silicate or zircon.

In order to further improve the bonding of zirconium silicate when suchdouble silicates are used, acid substances may be included. These may beadded to the mixture, in the form of liquids, prior to shaping, or themixture after shaping may be subjected to acid fumes. Examples of liquidacids are H2S04, HN03 or phose phoric acid. Examples of acid fumes areH01, S02 or fumes from H2504 (i. e. S03). Solutions. of such acid fumesmay also be employed (e. g. H01).

In addition to the zircon or zirconium silicate,

other materials may be included in the compositions of the presentinvention. For example, granular materials such as silica sand, naturalor synthetic corundum, or silicon carbide may be admixed therewith.

After the mixture is formed, it is fired at an elevated temperature,such as between 800 C. and 1500 0.

Having described the invention, the following examples are now given.Unless otherwise mentioned, parts are parts by weight.

Example 1 A sodium zirconium silicon citrate solution is prepared asfollows: Finely-milled zirconium silicate is decomposed by heating withan alkali such as sodium carbonate at a temperature of 900-950 C. toyield a product readily soluble in dilute acids. Other alkalis, such assodium hydrate, sodium peroxide or sodium sulfide, or mixtures thereof,may be used in place of sodium carbonate; or potassium compounds such aspotassium carbonate may be used. 100 parts of this roasted product,consisting of sodium zirconium silicate, are wet milled with 96 parts ofwater in a suitable ball mill until less than 0.5% remains on a 325 meshsieve when a sample is tested for fineness. The mill is discharged, andthe slurry thus obtained, which consists mainly of sodium zirconiumsilicate in water suspension, will have a composition approximately asfollows:

Per cent Zirconium (calculated as Zr0z) 20.65 Silicon (calculated asS102) 10.49 Sodium (calculated as NazO) 14.06 Water, etc 54.80

, 59.1 parts of citric acid are then dissolved in 63.5 parts of water atabout 80-90 0., and 100 parts of the above sodium zirconium silicateslurry are added by suitable dispensing equipment While stirring thecitric acid solution. The sodium zirconium silicate dissolves almostcompletely leaving a small amount of insoluble residue which ifrecovered will constitute less than two parts of the 100 parts of sodiumzirconium silicate slurry used. This represents a conversion ofapproximately 94% of the zircon originally used into dissolvedcondition. Whether this small amount of insoluble matter is removed fromthe citrate solution is of no importance; if retained the dried productwould be more or less opaque.

The solution formed has a slight acid reaction and in contact with ironhas a mild reactive efieot with the iron. I have found that if thesolution is neutralized by any suitable alkaline substanceammoniumhydrate for example,- and preferably made slightly alkaline, it thendoes not affect iron and may be handled without detriment in ironvessels. The neutralizing may be effected either before or afterremoving the insoluble residue.

After settling out the small amount of insoluble residue, theessentially clear neutral or slightly alkaline solution is then decantedand upon analysis has approximately the following composition:

Per cent Silicon (calculated as $102) 4.07 Zirconium (calculated asZlOz) (including small amounts of aluminum and rare earths) 1.96Titanium (calculated as TiOz) 0.02 Iron (calculated as F6203) 0.01Carbon (C) 8.21 Sodium (calculated as Na-zO) 5.95 Water 73.78

The solution has an index of refraction of 1490-1495 and a specificgravity of 1.325.

7 parts by weight of the above solution are mixed with 100 parts byweight of granular zircon (ZrSiOii),60+200 mesh in size. The mixture isformed into suitable shape by pressing into a suitable form and thendried. The shaped mass is then burned to about 1200 C. to form thefinished article which is a porous material consisting of ZrSiOi grainsbonded together by the residual products of the sodium zirconium siliconcitrate mainly sodium zirconium silicate.

The citrate solution referred to I have found to be an excellent bondingagent, effectively bonding throughout the temperature range from roomtemperature to the maturing point of the objects formed.

Example 2 The same procedure is followed as in Example 1 except that thesodium zirconium silicate slurry, before being added to the citric acidsolution, is freed from water-soluble material as follows: The waterdissolved material consists mainly of any excess alkali as well as smallamounts of sodium aluminate, and sodium silicate, traces of chrmium,vanadium, manganese, etc. which may be removed simply by separating thesodium zirconium silicate solids from the small amount of dissolvedmaterial by any suitable mechanical means. The water insoluble sodiumzirconium silicate is then brought back to the form of slurry bydilution with water, and the solution in citric acid effected in thesame manner as in the preferred direct treatment procedure, but reducingthe amount of citric acid in proportion to the amount of materialremoved.

This purification step may prove import-ant in case cruder ores are usedor in case of ores or materials in which there is an excess of siliconmineral.

Example 3 100 parts of granular zircon (ZrSiOr) -60+200 mesh in size arecompounded with 2 parts of sodium zirconium silicate having thefollowing Sufficient water is then added to make a stiff mixture whichis then mixed and shaped into the form of the desired finished article.A small amount of an acid substance, such as I-ICl, may be added withthe water to assist in setting the mixture. The formed object is thenburned at a temperature of about 1200 C. to form a porous article.

Example 4 A porcelain-like zircon body may be produced by mixing milledzircon (for example-325 mesh zircon) with the bonding agent as inExample 1, 2 or 3 and then burning the mix to a temperature high enoughto form a porcelain-like zircon material which in itself is non-porousor practically so.

Example An object of very large pores may be produced by crushing thematerial produced in accordance with Example 4, mixing with the bondingagent as in Example 1, 2 or 3, and firing at an elevated temperature asbefore.

Example 6 The same procedure is followed as in Example 1 except thatzirkite is used as a raw material in place of zircon. Free silica isadded until the ratio of ZI'O2 to S102 is approximately 65 to 35.

Porous masses formed of zirconium silicate in accordance with thepresent invention have a number of different uses. Some of these usesmay be enumerated as follows: (1) As filter plates in filtrations ofvarious kinds; (2) As diaphragms in electrolysis; (3) As instruments todisperse gases as these are led into liquids such as in the case ofabsorbing gases in liquids, the function being, by means of suitableconnections to the porous zircon object in the liquid, to force the gasthrough the multitude of pores and into the liquid in a multitude offine bubbles which are more readily absorbed than are the largerbubbles; (4) As separating plates for purpose of separating two liquidswhich are purposely brought together slowly; (5) As refractory objectsin combustion equipment having the effect of intimately contacting thecombustible gas with the gaseous oxidizing agent; (6) As an abrasivematerial; (7) As a super-refractory material for objects required tostand high temperatures.

In the appended claims such substances used as the bonding agents whichI have described comprise double silicates of zirconium and certainother metals, or materials that under the temperatures applied willdecompose to form such double silicates.

I claim:

1. A coherent fired zirconium silicate comprising zirconium silicateinterstitially bonded with a minor quantity of a double silicate ofzirconium and a metal taken from the group consisting of alkali metals,alkaline earth metals and magnesum.

2. A coherent fired zirconium silicate comprising zirconium silicateinterstitially bonded with a minor quantity of sodium zirconiumsilicate.

3. A coherent fired zirconium silicate comprising zirconium silicateinterstitially bonded with a minor quantity of a double silicate ofzirconium and a metal taken from the group consisting of alkali metals,alkaline earth metals and magnesium, together with the reaction productof an acid chosen from the group H3PO4, HCl, I-IzSOr, and HNOstherewith.

4. A coherent fired porous zirconium silicate comprising granularzirconium silicate interstitially bonded with the coalesced residue of asodium zirconium silicon citrate solution consisting mainly of sodiumzirconium silicate.

5. The method of making coherent zirconium silicate which comprisesmixing a major quantity of zirconium silicate with a minor quantity of amaterial taken from the class consisting of double silicates ofzirconium and a metal taken from the group consisting of alkali metals,alkaline earth metals and magnesium, and substances capable of formingsaid double silicates at an elevated temperature, and burning saidmixtureat an elevated temperature.

6. The method of making coherent zirconium silicate which comprisesmixing a major quantity of zirconium silicate with a. minor quantity ofa double silicate of zirconium and a metal taken from the groupconsisting of alkali metals, alkaline earth metals and magnesium, addingto said mixture an acid substance chosen from the group H3PO4, HCl,H2804, and HNO3 with sufficient water to form a stiff mixture, shapingto form, and burning the form at an elevated temperature.

7. The method of making coherent zirconium silicate which comprisesmixing a major quantity of zirconium silicate with a minor quantity of adouble silicate of zirconium and a metal taken from the group consistingof alkali metals, alkaline earth metals and magnesium, adding to saidmixture an acid substance chosen from the group H3PO4, HCl, H2804, andI-INOs with sufficient water to form a stifl mixture.

8. The method of making coherent porous zirconium silicates whichcomprises mixing granular zirconium silicate with powdered sodiumzirconium silicate in the ratio of about 100 parts of the granularzirconium silicate to 2 parts by weight of the sodium zirconiumsilicate, adding to the charge an acid substance chosen from the groupH3PO4, I-ICl, H2SO4, and HNOs with sufficient water to form a stiffmixture and shaping same to form, and burning the form at about 1200 C.

9. The method of making coherent zirconium silicate which comprisesmixing a major quantity of zirconium silicate with a minor quantity ofan aqueous solution of a substance capable of forming at an elevatedtemperature a double silicate of zirconium and a metal taken from thegroup consisting of alkali metals, alkaline earth metals and magnesium,shaping to form, and burning the form at an elevated temperature.

10. The method of making coherent porous zirconium silicates whichcomprises mixing granular zirconium silicate with a sodium zirconiumsilicon citrate solution, shaping the mixture to form and drying same,and then burning the dried form at temperatures between 800 and 1500 C.

11. The method of making coherent porous zirconium silicates whichcomprises maxing granular zirconium silicate with a sodium zirconiumsilicon citrate solution in the ratio of about 100 parts of the granularzirconium silicate to form 1 to 12 parts by weight of said citratesolution, shaping the mixture to form and drying same, and then burningthe dried form at temperatures between 800 and 1500 C.

CHARLES J. KINZIE.

